Security Policy Errors

How to Fix DMARC Failure for Internal Campaigner Emails in Microsoft 365

Chanuka Geekiyanage Oct 9, 2026 868 views

Question details

Users need to prevent Microsoft 365 from blocking internal mass emails sent via Campaigner due to DMARC authentication failures.

How to Fix DMARC Failure for Internal Campaigner Mass Emails

Product: Microsoft 365 / Exchange Online
Device & OS: not provided
Scenario: Sending internal mass email campaigns using the third-party vendor Campaigner to internal Microsoft 365 recipients.
Observed behavior: Microsoft 365 spam filters block the emails or flag them as spam due to SPF, DKIM, or DMARC alignment failures.

Before you start

Ensure you have Exchange Administrator access in Microsoft 365 and access to your domain's DNS management portal to update your DNS records.

Solution 1Recommended

Configure SPF and DKIM for Campaigner

Authenticate Campaigner to send on behalf of your domain so that emails pass Microsoft 365 DMARC checks.

The most secure and permanent way to resolve DMARC failures is to properly configure your domain's SPF and DKIM records. This aligns the visible 'From' domain with the authenticated domain.

Contact Campaigner Support

Reach out to Campaigner to obtain their official sending IP addresses and the necessary DKIM CNAME records or keys required for your domain.

Access DNS Settings

Update the SPF Record

Edit your existing TXT record for SPF to include Campaigner's specific IP addresses or their provided 'include' statement before the '~all' or '-all' mechanism.

Add DKIM Records

Create new CNAME records in your DNS zone using the DKIM information provided by Campaigner. Save all changes and wait for DNS propagation.

DNS Propagation: DNS changes can take anywhere from a few minutes to 24 hours to fully propagate globally.

Solution 2

Create an Exchange Mail Flow Rule

Implement a temporary workaround by creating a mail flow rule to bypass spam filtering for emails originating from Campaigner's verified IP addresses.

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Frequently Asked Questions

Why does Microsoft 365 block internal emails from third-party tools like Campaigner?

Microsoft 365 uses strict DMARC, SPF, and DKIM checks to prevent spoofing. If a third-party tool sends an email using your internal domain without proper DNS authentication, Microsoft 365 flags it as suspicious and blocks it or routes it to the junk folder.

What does Spam Confidence Level (SCL) -1 mean in Exchange?

Setting the SCL to -1 through an Exchange mail flow rule tells Microsoft 365 to bypass standard spam filtering for that specific message, ensuring it gets delivered directly to the recipient's inbox.

How do I check if my SPF and DKIM records are correctly aligned?

You can use online DNS lookup tools or review the message headers of a test email sent from Campaigner to your inbox. Look for the 'Authentication-Results' header to verify that it shows 'pass' for both SPF and DKIM alignment.

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